Recently, NO.sub.x, CO.sub.2, SO.sub.2 and the like existing in the atmosphere have become a serious environmental problem. The cause of NO.sub.x is exhaust gas discharged from automobiles and factories. In the natural world, the concentration of NO.sub.2 and NO is several ppb. On the other hand, in big cities, the concentration of NO.sub.2 and NO is 50 ppb at the maximum, which causes a serious social problem. The situation is the same in the case of CO.sub.2. Further, acid rain causes a serious problem. Air pollution caused by SO.sub.2 gas contained in the combustion gas discharged from factories could be one of the factors causing acid rain.
Recently, the size and weight of electronic apparatuses such as electronic computers, for example, personal computers, word processors, facsimiles, telephones, and notebook-type personal computers, tend to be reduced. In these small electronic apparatus, the problem of corrosion occurs. Conventional large-sized electronic computers are installed in air-conditioned environments, so that the problem caused by corrosion rarely occurs. However, small-sized electronic apparatuses are used in all environments. Therefore, not only H.sub.2 S, Cl and humidity but also NO.sub.x, SO.sub.2 and the like might affect those electronic apparatus.
The present invention provides a method by which these gases are simply collected and analyzed so that the environment can be monitored.
At present, there is provided a method to monitor the concentration of NO.sub.x for which an expensive large-sized automatic measuring apparatus is used. By the above method, the concentration of NO.sub.x is measured in the following manner: Into a Saltzman reagent in which phosphoric acid, sulfaninilic acid, and Nl naphthyl ethylene diamine hydrochloride are dissolved in distilled water, a predetermined amount of air containing NO.sub.x is sent by an air pump. When this reagent reacts with NO.sub.x, the color of the reagent changes to pink. The higher the concentration of NO.sub.x in the reagent is, the denser the color of pink becomes. Next, the reagent is exposed to light, and the concentration of the coloring liquid is measured by a value of the transmission factor.
However, this method is disadvantageous in that: it is not possible to measure the concentration of NO.sub.x at an arbitrary position; and further the period of time to collect data is so short that it is necessary to analyze a large amount of data to know an average concentration over a long period of time. Therefore, this method cannot be applied to many cases.
There is provided a method to monitor the concentration of CO.sub.2 for which an expensive large-sized automatic measuring apparatus and a semiconductor sensor are used. It is not possible to apply this measuring method at an arbitrary position. Further, the period of time to collect data is so short that a large amount of data must be analyzed to provide an average concentration over a long period of time. In order to measure the concentration of CO.sub.2 gas, a nondispersive infrared analyzer (NDIR) and a gas chromatograph (GC) are commonly used. Into those apparatus, the gas to be measured is introduced, and relative determination is performed in accordance with the absorption rate found from the light absorption coefficient. However, these methods can be applied to only limited locations, that is, in cities, where the measuring apparatus can be easily conveyed and a power source can be easily provided. In a mountainous area, forest or jungle, it is difficult to use these apparatuses.
In order to measure the concentration of SO.sub.2 gas, the following method has been known: An absorption solution is put in a collecting bottle, and the bottle is plugged with a cap having a bubbler. When the air in the collecting bottle is sucked by a collecting pump, the environmental air is introduced to the absorption solution, and SO.sub.2 gas in the air is trapped by the absorption solution in accordance with the method prescribed by JIS K-0103. After that, the absorption solution is chemically analyzed, and the obtained result is converted into the concentration of gas.
According to the aforementioned method, it is possible to collect only sulfur oxide so that the concentration of sulfur oxide can be accurately provided. However, an operator skilled in operating the entire apparatus is required for normally operating the power source to drive the air pump and for normally operating the collecting device. Therefore, the location and time for sampling are limited.
Further, the following measuring method has been known: After a filter paper has been soaked in a water solution of potassium carbonate, it is air dried. Then, the filter paper is left in an environment so as to collect SO.sub.2 gas, which is chemically analyzed and the obtained result is converted into the concentration. According to this alkaline filter paper method, only the filter paper must be set in a location where the environment is measured, so that the gas collecting work is simple. However, H.sub.2 S is collected in the form of SO.sub.3. Therefore, this method is essentially disadvantageous in that it is impossible to discriminate between SO.sub.2 and H.sub.2 S.
Accordingly, it is desired to provide a method to monitor the average concentrations of NO.sub.x, CO.sub.2 and SO.sub.2 at an arbitrary location over a long period of time.
In order to accomplish the similar object, the present applicant (Fujitsu Co., Ltd.) has developed and disclosed a method in Japanese Unexamined Patent No. Sho. 63-305232, by which the concentration of corrosive gas is monitored with a metallic test piece. However, according to this method, it is difficult to collect NO.sub.x and CO.sub.2, and further the obtained result is not accurate. Moreover, it is difficult to discriminate between SO.sub.2 and H.sub.2 S. Therefore, the accuracy cannot be improved.
It is desirable to improve the handling properties of test pieces and also to eliminate the causes to disturb the measuring condition when the test pieces are left in various measuring environments.
It is an object of the present invention to provide a method and means by which the average concentrations of NO.sub.x, CO.sub.2 and SO.sub.2 gases can be simply and accurately monitored in an environmental atmosphere at an arbitrary location with an inexpensive and small-sized apparatus.